This application is based on Patent Application No. 361,581/1997 filed on Dec. 26, 1997 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates generally to an image printing apparatus and a method, such as an ink-jet printing system or the like. More particularly, the invention relates to an image printing apparatus and a method performing a density correction for an image data upon forward printing and backward printing.
2. Description of the Related Art
A typical method for performing printing for cloth, wall paper and so on, is a screen cloth printing method for directly printing on a cloth or the like using a silk screen printing plate. In performing this method, each silk screen printing plate for each color used in an original image to be printed in a screen cloth printing apparatus is installed so that an ink of the corresponding color is directly transferred to the cloth or the like through mesh of the silk screen printing plate.
However, in such a screen cloth printing method, printing plates corresponding to ink colors are required to be prepared. Therefore, a large amount of process steps are required for preliminarily preparing the silk screen printing plate and many days are taken for completing the printing products. In addition, there are operations to blend inks for each color and registration adjustment of the silk screen printing plates for respective colors and so on are required. Furthermore, the screen cloth printing apparatus is bulky and becomes more bulky in proportion to the increase of number of colors to be used and therefore requires a large installation space. In addition, storage space of the silk screen printing plates is also required.
Therefore, there has been proposed a printing method of an ink-jet printing system for directly printing an image on a printing medium, such as a cloth, a wall paper and so on. The printing method in the ink-jet system is a method for printing the image on the printing medium by ejecting fine ink droplets toward the printing medium, such as cloth or the like from ejection openings (nozzles) provided in a printing head for ink-jet printing. With such printing method, screen printing plates required for the conventional screen cloth printing becomes unnecessary. As a result, process steps and days for forming the image on the cloth or the like can be significantly reduced. Also, down-sizing of the apparatus also becomes possible. Furthermore, an image information for printing can be stored in storage medium, such as tape, flexible disk, an optical disk or the like to exhibit superior storage ability of the image information. In addition, variation of color scheme, modification of layout, increasing and decreasing of magnification and so on for a current image can be performed easily.
Upon performing cloth printing by the ink-jet printing system, the cloth dyed object can be a natural fiber, such as cotton, silk, wool and the like, synthetic fiber, such as nylon, rayon, polyester and the like, mixed fiber spinning of those fibers. Accordingly, coloring agents for coloring these fibers are also in wide variety. For example, water insoluble dye or a dye having low solubility in water can be used, such as a dispersion dye for polyester fiber, a metal complex dye for wool, a vat dye or pigment for cotton. In order to prepare a water based ink from insoluble or low solubility coloring agent, fine particulate of chromogen is formed and dispersed in water by a dispersion agent to form emulsion.
Among the foregoing ink-jet type printing apparatus, in a serial type printing apparatus employing a serial scanning type taking a direction intersecting a transporting direction of the printing medium (auxiliary scanning direction) as a primary scanning direction, an image is printed by nozzles of the printing head mounted on a carriage moving in the primary scanning direction along the printing medium. After printing (forward printing) for one line, paper feeding (pitch feeding) for a predetermined amount is performed in the auxiliary scanning direction. Then, printing for the next line is performed in batch process (backward printing). By repeating these operations, printing on the entire printing medium can be performed. Printing can be further sped up by using an ink-jet type printing apparatus having a serial type printing head, in which a large number of ejection openings are arranged along the width direction of the printing medium.
Using such ink-jet type printing apparatus for cloth printing, the screen printing plate used for screen cloth printing becomes unnecessary to reduce process steps and days to print the cloth for down-sizing the apparatus.
However, in the ink-jet printing apparatus, a gap between the cloth and the printing head becomes greater in comparison with the normal printer for computer. In the cloth printing, since there are clothes of various textures, the large gap between the cloth and the printing is inherent.
Therefore, the peculiar problem for an on-demand type ink-jet printing apparatus may occur. That is to say, by a subsidiary liquid droplet generated upon primary droplet ejection, a difference in densities may occur between forward scanning printing and backward scanning printing in the primary scan of the printing head. This difference of density is regarded as one factor of degradation of the image quality.
This will be further explained hereinafter with reference to special example.
FIGS. 25A to 25G generally show liquid ejection process in a bubble jet type ink-jet printing. Hereinafter, respective steps in FIGS. 25A to 25G of the printing process will be explained in sequential order.
FIG. 25A shows a condition where an ink 1510 is filled within a nozzle 1500.
As shown in FIG. 25B, by applying an energy to an electrothermal transducer 1520 for a quite short period, the ink in the vicinity of the electrothermal transducer 1520 is abruptly heated to generate a fine bubble 1530.
As shown in FIG. 25C, the ink 1510 is evaporated abruptly to cause growth of the fine bubble 1530.
Then, as shown in FIG. 25D, due to expansion of the bubble 1530 maximum, the ink 1510 is pushed out.
As shown in FIG. 2E, the bubble 1530 is abruptly shrunk as being cooled by the ink 1510. Then, the pushed out ink becomes an ink droplet 1540 in a form of droplet.
As shown in FIG. 2F, the ink droplet 1540 is pushed out to fly in the direction of arrow.
As shown in FIG. 2G, the tail portion of the ink droplet 1540 becomes droplet form by surface tension.
Not limited to the bubble-jet printing, upon ejection of liquid droplet in an ink-jet printing in broader sense, the tail portion upon primary droplet ejection becomes an ink droplet 15 by surface tension of the ink per se, in addition to the primary droplet (ink droplet 1540) originally required for printing, subsidiary ink droplet (hereinafter referred to as satellite) is generated. Since the satellite is formed by shred of the tail portion extending from the primary droplet, it has been observed that flying speed thereof is lower than that of the primary droplet.
In serial scan printing, as long as performing printing in one path, either in forward side or backward side, the generated satellite constantly deposited in the same direction on the cloth to cause no problem in image designing. However, it is typical to perform reciprocal printing in order to achieve improvement of printing speed. Then, problem can be encountered by satellite.
On the other hand, it has been clear from observation that satellite flies with xe2x80x9can angle offset from the primary dropletxe2x80x9d. FIG. 26 shows comparison of the ejecting angle of the primary droplet and satellite. Assuming that a speed of a carriage mounting a printing head having the nozzles for ink ejection is V, the primary droplet ejected from the nozzle flies at the primary droplet speed V with the ejecting angle xcex8. In contrast to this, the satellite flies at a satellite speed VS with ejecting angle xcex8s. Here, xe2x80x9can angle offset from the primary dropletxe2x80x9d set forth above, is an angle xcex8a expressed by xcex8a=xcex8xe2x88x92xcex8S in FIG. 26.
FIGS. 27A and 27B a show dot deposited on the cloth by the primary droplet and satellite.
FIG. 27A shows the dot formed by printing in the forward scan. On the other hand, FIG. 27B shows the dot formed by printing in the backward scan. The flying angle of the satellite 1550 is offset in the extent of 1xc2x0 angle relative that of the primary droplet 1560 and flying speeds are different. Therefore, while the flying speed of the satellite 1550 generated in the forward scan is lower than that of the primary droplet 1560, the dot formed by satellite 1550 is hidden in the dot formed by the primary droplet 1560 as shown in FIG. 27A. In contrast to this, the satellite 1550 generated in the backward scan deposits at different position to the deposit position of the primary droplet 1560 as shown in FIG. 27B.
As set forth above, in the forward scan, since satellite 1550 deposit within the dot formed by the primary droplet 1560, colored area is held unchanged. However, in the backward scan, since the primary droplet 1560 and the satellite 1550 deposit at different positions, the colored area becomes primary droplet+satellite. Density in the ink-jet type printing is determined by colored area on the cloth namely, when ink deposition area is larger, density becomes higher correspondingly. Therefore, difference of the colored area in the forward scan and the backward scan should be perceived as difference of density.
As can be appreciated from the foregoing example, since a difference in densities between the forward scan and the backward scan becomes perceptible in the primary scan of the printing head, degradation of the image on the printing medium, such as cloth or the like, can be caused to make it difficult to perform high quality printing.
Therefore, it is an object of the present invention to provide a printing apparatus and a method which can eliminate difference between an image density upon forward scan and an image density upon backward scan, and can perform high quality image printing with avoiding influence of satellite.
In a first aspect of the present invention, there is provided an image printing apparatus performing printing of an image for a printing medium by reciprocating a printing head, comprising:
density difference correction signal generating means for generating a density difference correction signal for correcting a density difference between an image density upon forward path printing by the printing head and an image density upon backward path printing by the printing head;
storage means for storing the generated density difference correction signal; and
density conversion means for varying image density of image data for forward printing and backward printing depending upon stored density difference correction signal.
In a second aspect of the present invention, there is provided an image printing apparatus reciprocating a plurality of printing heads and performing overlay printing of an image for a printing medium by the combined scans of forward path and backward path of a plurality of the printing heads, comprising:
density difference correction signal generating means for generating a density difference correction signal for correcting a density difference by the combined scans of forward path and backward path of a plurality of the printing heads;
storage means for storing the generated density difference correction signal; and
density conversion means for varying image density of image data upon printing by the combined scans of the forward path and the backward path depending upon the stored density difference correction signal.
In a third aspect of the present invention, there is provided an image printing apparatus reciprocating a printing head to perform performing printing of an image for a printing medium, comprising:
printing means for printing test images in forward path scan and backward path scan of the printing head;
reading means for reading the printed test images;
density difference correction signal generating means for generating a density difference correction signal for correcting a density difference between the test image density upon forward path printing by the printing head and the test image density upon backward path printing by the printing head;
storage means for storing the generated density difference correction signal; and
density conversion means for varying image density of image data for forward printing and backward printing depending upon stored density difference correction signal.
In a fourth aspect of the present invention, there is provided an image printing apparatus reciprocating a plurality of printing heads and performing overlay printing of an image for a printing medium by the combined scans of forward path and backward path of a plurality of the printing heads, comprising:
printing means for printing test images by the combined scans of forward path and backward path scan of the printing heads;
reading means for reading the printed test images;
density difference correction signal generating means for generating a density difference correction signal for correcting a density difference of the test images formed by the combined scans of forward path and backward path of a plurality of the printing heads;
storage means for storing the generated density difference correction signal; and
density conversion means for varying image density of image data upon printing by the combined scans of the forward path and the backward path depending upon the stored density difference correction signal.
In a fifth aspect of the present invention, there is provided an image printing method performing printing of an image for a printing medium by reciprocating a printing head, comprising the steps of:
generating a density difference correction signal for correcting a density difference between an image density upon forward path printing by the printing head and an image density upon backward path printing by the printing head; and
varying image density of image data for forward printing and backward printing depending upon generated density difference correction signal.
In a sixth aspect of the present invention, there is provided an image printing method reciprocating a plurality of printing heads and performing overlay printing of an image for a printing medium by the combined scans of forward path and backward path of a plurality of the printing heads, comprising the steps of:
generating a density difference correction signal for correcting a density difference by the combined scans of forward path and backward path of a plurality of the printing heads; and
varying image density of image data upon printing by the combined scans of the forward path and the backward path depending upon the generated density difference correction signal.
In a seventh aspect of the present invention, there is provided an image printing method reciprocating a printing head to performing printing of an image for a printing medium, comprising the steps of:
printing test images in forward path scan and backward path scan of the printing head;
reading the printed test images;
generating a density difference correction signal for correcting a density difference between the test image density upon forward path printing by the printing head and the test image density upon backward path printing by the printing head; and
varying image density of image data for forward printing and backward printing depending upon generated density difference correction signal.
In an eighth aspect of the present invention, there is provided an image printing apparatus reciprocating a plurality of printing heads and performing overlay printing of an image for a printing medium by the combined scans of forward path and backward path of a plurality of the printing heads, comprising the steps of:
printing test images by the combined scans of forward path and backward path scan of the printing heads;
reading the printed test images;
generating a density difference correction signal for correcting a density difference of the test images formed by the combined scans of forward path and backward path of a plurality of the printing heads; and
varying image density of image data upon printing by the combined scans of the forward path and the backward path depending upon the generated density difference correction signal.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings.